Investigation of the mechanical and durability properties ofrecycled aggregate geopolymer composites containing metazeolite

Kaolinite clay, metakaolin (MK), fly ash (FA), and ground granulated blast furnace slag (GGBFS) are used as aluminosilicate-based materials in geopolymer mortar samples (GMs). In addition to these materials, meta products (bentonite, kaolin, and zeolite) can also be included among the components of GMs. Depending on the type of clay, dehydration and dehydroxylation are achieved at certain degrees through the calcination process. In this way, metastable, nearly amorphous aluminosilicate phases, which are soluble in alkaline solutions, are formed. In this study, GMs reinforced with synthetic fibers based on metazeolite (MZ) and GGBFS containing recycled concrete aggregate (RCA) and aluminum sludge (AS) were produced. The ratio of Na₂SiO₃/NaOH was set at 2:1, and the activator/binder ratio was determined as 0.95 for NaOH and Na₂SiO₃, which were used together as alkaline activators. Different molarity ratios (8M, 10M, 12M, and 14M) and various mixture ratios (25% MZ + 75% GGBFS, 50% MZ + 50% GGBFS, 75% MZ + 25% GGBFS, and 100% MZ) were tested, and the durability properties of these mixtures were investigated. Considering various criteria (durability, environment, and economy), the 50MZ + 50GGBFS series at 12M was selected, and the physical and mechanical properties were examined for 7 and 28 days by adding 10%, 20%, and 30% AS with RCA replacement in this series. The results showed that the 50MZ + 50GGBFS/30AS series exhibited the best durability properties compared to the 50MZ + 50GGBFS series. Therefore, in this series, different types of fibers such as polyethylene fiber xviii (PEF), polyamide fiber (PAF), and basalt fiber (BF) were added in ratios of 0.25%, 0.5%, 0.75%, 1%, 1.5%, and 2%. In the next step, physical properties such as unit weight, porosity, and water absorption, as well as mechanical properties (compressive strength, flexural strength, direct tensile strength, splitting tensile strength), and 28-day wear resistance tests were performed. Microstructural characterization was carried out using SEM/EDS and XRD analyses. The microstructural properties showed that the series containing 30% AS was denser than the other series. The highest strength values were also achieved in samples containing 30% AS. However, workability significantly decreased at this level. With fiber reinforcement, the best results in terms of physical and mechanical properties were obtained respectively from BF > PAF > PEF fibers. The highest compressive strength increase was observed in the 0.5% BF-reinforced sample with a 27,2% increase compared to the reference, while this difference increased to 167% in flexural strength. The best direct tensile strength increase was observed in the sample containing 0.5% PAF with a 53% increase. The highest wear resistance volume losses for all fiber-reinforced GMs were observed in samples containing 1.5% PAF and BF. In post-high-temperature strength, samples containing BF showed the best performance up to 400°C, whereas when temperatures reached 800°C, BF and PAF samples completely disintegrated. It was observed that BF and PEF reinforcements prevented crack propagation in GMs against freeze-thaw effects and maintained their structural integrity. The best mechanical performance against sulfate effects was observed in samples containing PEF, while PAF-containing samples were more affected by the harmful effects of sulfate